Space agencies pinpoint polar ice sheet damage

The midnight sun casts a golden glow on an iceberg and its reflection in Disko Bay, Greenland, where ice sheet mass loss was five times higher in 2011 than it was in 1992. Much of Greenland’s annual mass loss occurs through 'calving' of icebergs such as this. Credit: Ian Joughin.

The midnight sun casts a golden glow on an iceberg and its reflection in Disko Bay, Greenland, where ice sheet mass loss was five times higher in 2011 than it was in 1992. Much of Greenland’s annual mass loss occurs through ‘calving’ of icebergs such as this. Credit: Ian Joughin.

47 scientists from 26 key laboratories across the world. 10 satellite missions flown over a period of 20 years, whose data adds up to 51 years’ worth. This giant effort looks to have squashed stubborn uncertainty surrounding one key climate question: How quickly are ice sheets resting on land masses at the North and South Poles shrinking? The international team has now found that Greenland’s mass loss is five times as fast as it was in 1992. Overall loss rates in Antarctica are roughly constant in this period, though the east of the continent is actually gaining ice. Over the past 20 years, the polar ice sheets have added 11 mm to sea level rise across the world, one-fifth of the total rise seen in that time.

“Our new estimates are the most reliable to date and they provide the clearest evidence yet of polar ice sheet losses,” said Andrew Shepherd from the University of Leeds, UK, co-leader of the project. “They also end 20 years of uncertainty concerning changes in the mass of the Antarctic and Greenland ice sheets and they’re intended to become the benchmark dataset for climate scientists to use from now on.”

Until the early 1990s, climate researchers expected that mass lost by ice sheets in Greenland as the planet warmed would be balanced by that gained by Antarctica. But measurements showed that both melting and ‘calving’ of icebergs could be speeding up at both poles. This meant the UN’s Intergovernmental Panel on Climate Change (IPCC) couldn’t put an upper limit on what ice sheets might add to sea levels in its last major report on global warming in 2007. And the overall picture has been confused, as efforts to measure whether ice sheets are shrinking or growing have given differing results. Since 1998, there have been 29 different estimates of changes in ice sheet mass. “Taken all of the past studies together, the recent global sea level contribution due to Antarctica and Greenland may have been anywhere between a 2 mm per year rise and a 0.4 mm per year fall,” Andrew told a press conference yesterday. At a workshop in 2010, the IPCC said it was concerned that no further progress would be made by its next report, due in 2014. Read the rest of this entry »

Advertisements

Global view answers ice age CO2 puzzle

Paleoclimate researcher Jeremy Shakun. Credit: Harvard University

Paleoclimate researcher Jeremy Shakun. Credit: Harvard University

Previous data suggesting that the world started warming out of the last ice age before CO2 levels in the atmosphere started rising don’t show the full picture. That’s according to US, French and Chinese scientists who have added to those Antarctic measurements with more taken from 80 locations across the globe. Harvard University’s Jeremy Shakun and colleagues show the greenhouse gas rises before temperature, supporting the case that CO2 drove climate change then, as it is now. “This provides a very tangible example of what rising CO2 can mean for the climate over the long term,” Jeremy said.

In the 1980s, researchers began building the history of CO2 in the atmosphere from cylinders of ice drilled from the Antarctic. Bubbles in the ice contain air from the time they formed, which researchers can measure. They can also figure out how old the ice holding the bubbles is from how deep it is in the core. And finally they can also work out temperature from the amount of the different forms, known as isotopes, of elements like hydrogen, carbon and oxygen in the ice. That’s because the temperature at which the snow that eventually became the ice formed affects how much of each it contains. And because some isotopes are radioactive and decay to a more stable isotope with time, studying them gives scientists another way to check the ice’s age.

The 800,000 year record of atmospheric CO2 from Antarctic ice cores, and a reconstruction of temperature based on hydrogen isotopes in the ice. The current CO2 concentration of 392 parts per million (ppm) is shown by the blue star. Credit: Jeremy Shakun/Harvard University

The 800,000 year record of atmospheric CO2 from Antarctic ice cores, and a reconstruction of temperature based on hydrogen isotopes in the ice. The current CO2 concentration of 392 parts per million (ppm) is shown by the blue star. Credit: Jeremy Shakun/Harvard University

Such methods show temperature and CO2 levels rising and falling together for 800,000 years, Jeremy told journalists over the phone on Tuesday. “The question is: Which is the cause and which is the effect?” he asked. “If you look up close you see temperature changed before CO2 did. This is something the global warming skeptics have jumped on to say, ‘Obviously CO2 doesn’t cause warming because it came after the warming in these records’. But these ice cores only tell you about temperatures in Antarctica. For the same reason that you don’t look at just one thermometer from London or New York to prove or disprove global warming, you don’t want to look at just one spot in the map to reconstruct the past either.” Read the rest of this entry »

Climate forces penguin populations into a dive

Ice-loving Adélie penguins, once thought to be more at risk than ice-avoiding chinstrap penguins but actually faring better as the climate changes, in Admiralty Bay, Antarctica. Credit: Lenfest Ocean Program

Ice-loving Adélie penguins, once thought to be more at risk than ice-avoiding chinstrap penguins but actually faring better as the climate changes, in Admiralty Bay, Antarctica. Credit: Lenfest Ocean Program

Dwindling food supplies, caused by climate change, are threatening two species of penguin. Adélie and chinstrap penguins are both suffering thanks to falling availability of tiny shrimp-like crustaceans called krill that they eat. This is contrary to previous predictions, explained George Watters, director of the US National Oceanic and Atmospheric Administration (NOAA)’s Antarctic Ecosystem Research Division. That’s because those predictions directly link the amount of sea ice cover to the number of penguins.

“The prevailing ‘sea-ice hypothesis’ would say that chinstrap penguins might be expected to benefit from climate change because they are “ice-avoiding” penguins,” Watters told Simple Climate. By contrast, “ice-loving” Adélie penguin populations had been expected to fall as the planet warms and ice cover decreases. “But we’re showing that in fact the populations of both species are declining,” Watters said. “We think that the the availability of krill is governing the decline of both animals.”

The sea-ice theory developed from some of the earliest penguin population studies in the 1970s and 1980s, showing that Chinstrap penguin populations were increasing as Adélie penguins decreased. The team that did that work included Wayne Trivelpiece, lead author of the Proceedings of the National Academy of Sciences USA paper published on Monday that now shows both species are in decline. Both studies involved extensive fieldwork in the world’s coldest continent. “Wayne has been going since the Antarctic was invented,” Watters joked. Read the rest of this entry »

2010’s European heatwave unmatched in centuries

A thermometer in Moscow, where 2010's heatwave had a particulalrly great impact, on August 6 2010. Credit: Timon91/Flickr

A thermometer in Moscow, where 2010's heatwave had a particulalrly great impact, on August 6 2010. Credit: Timon91/Flickr

Europe has experienced two heatwaves in the past decade unlike any experienced in the previous 500 years, and is set to see more in coming decades. The fires that scorched Russia last year were part of a heatwave hotter and even more widespread than the previous record event in 2003. “What was really striking was that there was another such enormous heatwave in Europe in such a short period,” explained Erich Fischer. Together with four other European scientists, the Swiss Federal Institute of Technology, ETH Zurich, researcher has found that major heatwaves are set to become five to ten times more likely over the next 40 years. Yet despite this, another event like 2010’s is unlikely to occur until after 2050.

In a paper published in leading academic journal Science on Thursday, the Portuguese, Spanish, Swiss and German scientists analysed the significance of last summer’s average temperatures against three different historical temperature records. Two sets together provide measured daily average temperatures across Europe back as far as 1871, while the third reconstructs average temperatures for each season back to 1500. “For 500 years further back, we use tree rings, plus ice cores, plus documentary evidence,” Fischer told Simple Climate. Tree rings show how temperatures in a given year have affected the trees’ growth rates. Likewise, ice cores show how temperatures influenced ice sheets in places like Greenland and the Arctic through time, while documentary evidence speaks for itself. “In Europe, there’s many places where people already were interested back in the 16th and 17th century in what’s going on with the weather and climate and so they would be documenting these,” Fischer noted. Read the rest of this entry »

Ice age rethink puts warming into context

A 10 cm diameter ice core from Antarctica, drilled down to a depth of 2,250 m, which is more than 150,000 years old. The core is cleaned, measured, and catalogued after drilling. Image: Hans Oerter, Alfred Wegener Institute

A 10 cm diameter ice core from Antarctica, drilled down to a depth of 2,250 m, which is more than 150,000 years old. The core is cleaned, measured, and catalogued after drilling. Image: Hans Oerter, Alfred Wegener Institute

Both the northern and southern hemispheres’ climates – particularly coming into and out of ice ages – may be driven by energy falling directly on them from the sun. That might not sound surprising, but scientists have made just such a claim this week, challenging a fundamental theory of climate held since the 1970s. While it shows climate researchers are willing to question their assumptions, that claim does not undermine the idea that humans are causing climate change, explains Thomas Laepple.

Laepple, a researcher at the Alfred Wegener Institute (AWI) for Polar and Marine Research, Bremerhaven, Germany, makes his claim in relation to when ice ages happen. Our understanding of why they have occurred in the patterns in which they have, known as the glacial-interglacial cycle, is hampered by the mists of time. “There is a significant difference in looking at the glacial-interglacial cycle and the modern climate,” Laepple told Simple Climate. “In the glacial-interglacial cycle we are really digging into the dark, things are built on much less evidence.”

The fundamental understanding that Laepple and his AWI colleagues have challenged is related to the Milankovitch theory, devised by Serbian geophysicist Milutin Milanković in the early 20th century. “He was stating that changes in the orbit of the Earth around the sun are influencing the incoming radiation and this is the pacemaker for glacial-interglacials,” Laepple explained. “There is no doubt about this. The question is just: ‘How does it work?’” Read the rest of this entry »

Simple Climate poll part 4: The effects of change

A cloud forest habitat in southern Peru where lizard species are found. Certain lizards in these habitats are at risk of extinction due to climate warming. Credit: Ignacio De la Riva.

A cloud forest habitat in southern Peru where lizard species are found. Certain lizards in these habitats are at risk of extinction due to climate warming. Credit: Ignacio De la Riva.

The impact that climate change will have on the world is what makes it such a crucial issue, and makes it important to understand. Consequently, when I have asked scientists what the situation is with climate change this year, some have given me an explanation based on the effects that they’ve seen or expect.

I’ve gathered these answers together as the last group of explanations that I’m summarizing in the Simple Climate end of year polls. These polls are a way for you to help me with one of the aims of my blog – producing a single, simple explanation of climate change. Please read them and then vote for your favourite and/or comment at the end. Also, if you haven’t already voted in them, the first three polls are still ongoing. The first includes direct explanations of the physics underlying climate change, the second one-line and metaphorical explanations, and the third includes attempts to explain it at a personal level. The winner from each poll will then go into a final poll-to-end-all-polls at the end of the year. Happy voting! Read the rest of this entry »

Prehistoric CO2 double-up gives warming data

Electron microscopic picture of microfossils found in drill cores of sediments dating back 40 million years. By studying the remains of such marine plankton - and particularly compounds they produce called alkenones - scientists gain an accurate perspective of past climate change. Earlier, members of the same research team showed that the Arctic Ocean was colonized by similar types of tropical plankton. Scale bar is 20 millimetres, or 0.02 millimetres. Credit: Appy Sluijs

Electron microscopic picture of microfossils found in drill cores of sediments dating back 40 million years. By studying the remains of such marine plankton - and particularly compounds they produce called alkenones - scientists gain an accurate perspective of past climate change. Earlier, members of the same research team showed that the Arctic Ocean was colonized by similar types of tropical plankton. Scale bar is 20 millimetres, or 0.02 millimetres. Credit: Appy Sluijs

The first direct evidence supporting the idea that a recently-discovered period of global warming, one of the hottest in Earth’s history, was caused by CO2 has been published this week. Before the Middle Eocene Climatic Optimum (MECO), which occurred 40 million years ago, temperatures were much higher than today, but steadily falling. However, the MECO was a 400,000 year warming reversal of this trend. Researchers from the Netherlands and UK have now shown that it was accompanied by at least a doubling in atmospheric CO2 levels. Utrecht Univesity’s Peter Bijl and his colleagues also provide cautious estimates for just how much warming can be expected from adding CO2 in top journal Science this week.

Scientists already suspected that the approximately 4°C MECO temperature rise was caused by CO2. “There are only three ways to cause a large and lasting increase in Earth’s average surface temperature,” pointed out Paul Pearson from Cardiff University, UK, who was not involved in the study. “Turn up the heat from the Sun, reflect less sunlight back into space, or trap more heat in the atmosphere.” The heat from the Sun is relatively stable, Pearson comments in a separate article in this week’s Science giving his perspective on the research. Changes in the Earth’s reflectivity due to melting ice tend to happen after climate change has already begun, making greenhouse gases that trap heat around the Earth a likely culprit. Read the rest of this entry »